Colours underneath bleeding through when painting
Your model consists of at least two separate meshes. 

Right now, the front of the coaster uses the same texture as the seats, which means you have to create either a new material for it or you need to adjust the UV layout for both meshes so they don't overlap. 

One possible solution to use one material (and one texture) for all the meshes in your model would be using a Texture Atlas. 

If you want to use two separate textures, you need to set up a separate material for each mesh.